You actually have most of the answers correct.
E is the origin
D is the x axis
A is the y axis
B is at coordinates (1, 3)
C is at coordinates (3, 1)
*remember you go across on the graph x axis and then up y axis.
He will have 30 % in 2 years which is 30.00 dollars
For this case we have the following equation:

Deriving we have:

We match zero:

We clear the value of x:

Then, we substitute the value of x in the equation of the parabola:

Thus, the vertex of the parabola is the ordered pair:
Answer:
The vertice is: